As Whale said, we’re not psychic, but neither are you.
Why don’t you go out to your investment property and take a gander yourself?
Tenants often do not adequately describe a problem (the exhaust fan’s not working).
Property “Managers” don’t personally inspect reported problems.
Your electrician obviously could see the ventilation fan blades turning and pondered whether there is a blockage.
The SP’s ventilation “expert” is no expert if he states it’s impossible to tell whether the duct is blocked or not. Wasn’t that why he was sent?
The SM is no “expert” in common sense to suggest you spend $1500 on a more powerful exhuast system if they haven’t positively determined the duct is not blocked.
Last, and not least, landlords seldom know what tenants get up to in their leased premises.
Perhaps the filter on the exhaust fan has merely been blocked by fluff from their fluffy luxurious bath sheets.
Perhaps they take hour-long conjugal sauna sessions in the en-suite.
As this is an en-suite, such activity would also fill the bedroom with steam, causing condensation on the window, so perhaps your other problem, the reported window “leak” is nothing to do with the nearby (?) downpipe at all.